Refrigeration Cycle

ABSTRACT

Provided is a refrigeration cycle wherein a compressor, a condenser, a depressurizing/expanding means and an evaporator are provided. The refrigeration cycle uses R1234 as a refrigerant, and has an oil separating means, which forcibly separates the refrigerant and oil one from the other, in a two-phase separation region wherein the refrigerant and the oil exist in a separated state without being dissolved with each other. The refrigerant and the oil can be forcibly separated suitably at a suitable position even when the refrigerant is changed to the new refrigerant R1234yf, and the refrigeration cycle can be operated at a high efficiency as a whole.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a refrigeration cycle, and specificallyrelates to a refrigeration cycle which can be operated at a highefficiency as separating refrigerant and oil suitably for a case using anew refrigerant.

BACKGROUND ART OF THE INVENTION

A refrigeration cycle as used in an automotive air conditioning system,has a basic configuration as shown in FIG. 7. In FIG. 7, refrigerationcycle 101 has compressor 102 compressing refrigerant, condenser 103condensing compressed refrigerant, expansion valve 104 as adepressurizing/expanding means for depressurizing and expandingcondensed refrigerant and evaporator 105 evaporating depressurized andexpanded refrigerant. The refrigerant is circulated in refrigerationcycle 101 as changing its state. In such refrigeration cycle 101, therefrigerant sometimes contains lubricating oil, such as an oil made fromPAG [polyalkylene glycol], so as to enhance durability of compressor102, for example. When using refrigerant and oil, known is a method thatthe oil, which has been separated from refrigerant by an oil separatorprovided at an appropriate position, is returned to a compressor whichrequires to be lubricated, without being brought into a heat exchangeras far as possible, so that a heat transfer obstruction derived from anoil adhesion in a heat exchanger, such as evaporator 105, in the cycleis suppressed. Actually, the oil separator is not provided in most casesbecause the refrigerant R134a, which is a typical refrigerant atpresent, has a good compatibility with PAG oil.

For the R134a, etc., as a conventional typical refrigerant, research anddevelopment for a new refrigerant is being performed as disclosed inNon-patent document 1, aiming at further improvement of the globalwarming potential (GWP), etc. R1234yf has been recently announced as thenew refrigerant aiming such an improvement. And the research anddevelopment can be performed even for the application to a refrigerationcycle used in an automotive air conditioning system, etc.

PRIOR ART DOCUMENTS Non-Patent Document

-   Non-patent document 1: Refrigeration, Vol. 83, No. 965, March issue,    2008

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, because the new refrigerant R1234yf is less compatible with thePAG oil than R134a, a trouble that liquid refrigerant and oil areseparated at high-pressure side in the refrigeration cycle might becaused. In other words, in a case where the new refrigerant R1234yf isused in the refrigeration cycle as shown in FIG. 7, caused might be atrouble that the R1234yf is compatible with PAG oil at low-temperatureand low-pressure side (COMPATIBLE REGION) while the refrigerant and theoil tend to be separated at high-temperature and low-pressure side(TWO-PHASE SEPARATION REGION), as seen from an example of the operatingcondition for comparatively high load shown in FIG. 6. Once the oil isseparated from the refrigerant in the middle of a refrigerantcirculation route, the oil sometimes does not return to the compressorand loses the confidence of the compressor durability.

In addition, because an automotive air conditioning system with R134arefrigerant is usually provided with a sight glass, through which therefrigerant behavior can be monitored, in a liquid line of therefrigeration cycle, excess and deficiency of the refrigerant can bedetected. However, in a case where the new refrigerant R1234yf is used,the above-mentioned trouble that the liquid refrigerant and the oil areseparated in the middle of the refrigerant circulation route might becaused, and once the sight glass mists or is stained with the separatedoil, the excess and deficiency of the refrigerant cannot be detectedwith the sight glass in most cases.

Accordingly, focusing on the above-described troubles in a case wherethe new refrigerant R1234yf is used, an object of the present inventionis to make a refrigeration cycle capable of being operated at a highefficiency as a whole, as properly separating the refrigerant and theoil by compulsion at a proper position even when the refrigerant isreplaced by the new refrigerant R1234yf, as preferentially returning theseparated oil to a site such as a compressor which requires to belubricated, without possibly supplying the oil to a heat exchanger,etc., which should not be supplied with an oil.

Further, another object of the present invention is to make arefrigeration cycle capable of properly detecting the excess anddeficiency of the refrigerant through a sight glass which is provided ina liquid line of the refrigeration cycle even in a case where the newrefrigerant R1234yf is used.

Means for Solving the Problems

To achieve the above-described object, a refrigeration cycle accordingto the present invention is a refrigeration cycle having a compressorfor compressing refrigerant, a condenser for condensing compressedrefrigerant, a depressurizing/expanding means for depressurizing andexpanding condensed refrigerant, and an evaporator for evaporatingdepressurized and expanded refrigerant in this order in a refrigerantflowing direction, characterized in that R1234yf is used as therefrigerant, and an oil separating means for forcibly separating therefrigerant and oil one from the other is provided in a two-phaseseparation region, in which the refrigerant and the oil exist in aseparate state without being dissolved with each other, present in aroute from an exit side of the compressor to thedepressurizing/expanding means. The condenser in the present inventionconceptually includes a so-called “subcool condenser” which has asubcooled region where the refrigerant is condensed into a subcooledliquid refrigerant in a condenser, in addition to a normal condenser.

Namely, an oil separator is not necessary to be provided in most caseswhere R134a is used as a refrigerant, however, in the present inventionwhere the new refrigerant R1234yf is used, an oil separating means isprovided in a certain region, which means the above-described two-phaseseparation region, in a refrigeration cycle so as to separate therefrigerant and the oil by compulsion. The two-phase separation regionis suitable as a place to separate the oil. The two-phase separationregion is, in other words, a region where the refrigerant and the oilare being separated without special operation. The present inventionuses this region as an underhanded way. As described above, the oilshould not go through the heat exchanger as far as possible. However ina case where the refrigerant is in a gaseous state, the gaseous stateregion at an inlet side of the condenser is affected by the oil as wellthough even a conventional refrigerant is slightly compatible with theoil. Therefore in the present invention, it is preferable that the oilis separated in the two-phase separation region, especially at aposition between the condenser and the depressurizing/expanding means(from the outlet of the gaseous region in the condenser to the inlet ofthe depressurizing/expanding means), and in this region the oilseparating means is further preferably provided. By separating therefrigerant and the oil properly by compulsion in the two-phaseseparation region with various methods described later, the separatedoil, without passing through a heat exchanger at a downstream side, canbe returned to the compressor, etc., which requires to be lubricated.Consequently, the fear to cause a heat transfer obstruction derived fromthe oil adhesion in the heat exchanger can be reduced so that therefrigeration ability and the coefficient of performance of therefrigeration cycle can be improved, and additionally, the lubricationin the compressor, etc., can be always performed in a good condition, soas to get rid of the fear as to the durability.

In order to return the oil to the compressor, an oil return line forreturning oil separated by the oil separating means to the compressormay be provided between the oil separating means and the compressor. Forperforming the oil return, a capillary tube can be connected to acrankcase of the compressor and the oil can be returned directly.

If a sight glass is provided at a certain position in a liquid line atdownstream side of the oil separating means in a refrigerant circulationdirection, because most oil has already been separated and removed fromthe refrigerant passing through the site where the sight glass isinstalled, the oil, which has existed together with the refrigerant in astate separated from the refrigerant, can be prevented from making thesight glass mist, so that the refrigerant behavior can be clearlymonitored through the sight glass and the excess and deficiency of therefrigerant can be properly detected by the monitoring.

As described above, PAG oil made from polyalkylene glycol can be used asthe oil. In the two-phase separation region where the oil separatingmeans is provided, and specifically in a region from the condenseroutlet to the decompression/expansion means inlet, the refrigerant isusually in a liquid state, and its specific gravity of the refrigerantR1234yf is less than that of PAG oil, as shown in Table 1. In otherwords, the oil forms a layer below the refrigerant when separated bycompulsion. Therefore, if the separated oil is flowed out from the lowerside in a vertical direction and if the oil separating means is disposedat a position higher than the compressor in a vertical direction, theseparated oil can be easily returned to the compressor. Such a verticalposition relation between the oil separating means and the compressor iseffective in a case where the specific gravity of the oil is greaterthan the specific gravity of the refrigerant R1234yf, and isspecifically effective when the oil is PAG oil.

TABLE 1 Specific gravity R1234yf 0.97 R134a 1.08 PAG 1.00

The oil separating means itself can have various configurations. Forexample, it is possible that the oil separating means has a centrifugalseparation means for separating the refrigerant and the oil bycentrifuging the refrigerant and the oil, that the oil separating meanshas a collision separation means for separating the refrigerant and theoil by a collision of the refrigerant and the oil, or that the oilseparating means has a trap separation means for separating therefrigerant and the oil by trapping the oil from the refrigerant and theoil.

Further, it can have a combination of the above-describedconfigurations. For example, it is possible that the oil separatingmeans has a centrifugal separation means for separating the refrigerantand the oil by centrifuging the refrigerant and the oil and a trapseparation means for separating the refrigerant and the oil by trappingthe oil from the refrigerant and the oil or that the oil separatingmeans has a collision separation means for separating the refrigerantand the oil by a collision of the refrigerant and the oil and a trapseparation means for separating the refrigerant and the oil by trappingthe oil from the refrigerant and the oil.

In particular, if the trap separation means is provided at the lowestposition of the oil separator and the oil is trapped at the position ofthe trap separation means, the separated oil can be prevented fromflowing into a liquid refrigerant lifting tube, etc., which is locatedabove.

Also, it is preferable that a temporary storage section for separatedoil is provided at a lower position in a vertical direction in the oilseparating means. When such a temporary storage section is provided,because the separated oil is returned to a desirable destination from atemporary storing condition where a certain amount of the separated oilis stored, a stable oil return can be performed and the oil return linecan be sealed by the oil in the temporary storage section, so that therefrigerant can be prevented from undesirably flowing into the oilreturn line.

Also, it is preferable that an exit for separated oil is provided at alower end in a vertical direction of the oil separating means. Such aposition of the exit for the oil is effective specifically in a casewhere the specific gravity of the oil and the specific gravity of therefrigerant R1234yf have the same magnitude relation as describedbefore.

The refrigeration cycle according to the present invention is basicallyapplicable to any refrigeration cycle where the new refrigerant R1234yfmay be used, and is suitable as a refrigeration cycle in an automotiveair conditioning system which requires to be operated at high efficiencyand to have long-term high durability of the compressor, etc.

Effect According to the Invention

The refrigeration cycle according to the present invention makes itpossible to improve the durability and the reliability of the compressorin a refrigeration cycle using the new refrigerant R1234yf. Further,basically the oil is not circulated through the oil separating meansproviding section in the refrigeration cycle, so that the fear to causea heat transfer obstruction by the oil adhesion in a downstream heatexchanger is reduced, so as to improve the refrigeration ability and thecoefficient of performance of the refrigeration cycle. Furthermore, thebehavior of the refrigerant can be surely monitored by a sight glassprovided in the liquid line, so as to surely detect the excess anddeficiency of the refrigerant thereby.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a systematic equipment diagram of a refrigeration cycleaccording to an embodiment of the present invention.

FIG. 2 is a schematic framework showing an example of an oil separatingmeans in the present invention.

FIG. 3 is a schematic framework showing another example of an oilseparating means in the present invention.

FIG. 4 is a schematic framework showing yet another example of an oilseparating means in the present invention.

FIG. 5 is a schematic framework showing yet another example of an oilseparating means in the present invention.

FIG. 6 is a characteristic diagram showing an example of phase state forthe new refrigerant R1234yf.

FIG. 7 is a systematic equipment diagram of a conventional refrigerationcycle.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments of the present invention will beexplained as referring to figures.

FIG. 1 shows an equipment layout of a refrigeration cycle according toan embodiment of the present invention. As shown in the figure,up-and-down direction means the vertical direction X. Therefore, the topside in the figure means the highest position in the vertical direction,while the bottom side in the figure means the lowest position in thevertical direction. Refrigeration cycle 1 has compressor 2 compressingrefrigerant, condenser 3 condensing compressed refrigerant, expansionvalve 4 as a depressurizing/expanding means depressurizing and expandingcondensed refrigerant and evaporator 5 evaporating depressurized andexpanded refrigerant in this order in the refrigerant flowing direction(in the arrow direction), like the basic configuration shown in FIG. 7,wherein R1234yf is used as a refrigerant and oil separator 6 as an oilseparating means which separates the refrigerant and the oil bycompulsion is provided in a two-phase separation region, such as thetwo-phase separation region shown in FIG. 6, where the refrigerant andthe oil exist separately without being dissolved with each other in aregion from the outlet side of compressor 2 to the inlet of expansionvalve 4. In this embodiment, oil separator 6 is provided betweencondenser 3 and expansion valve 4 in the two-phase separation region.Oil separator 6 and compressor 2 are connected to each other with oilreturn line 7 which returns the oil forcibly separated by oil separator6 to compressor 2. A capillary tube can be used for oil return line 7,and one end of the capillary tube can be connected directly to thecrankcase of compressor 2, etc., so as to return the oil directly to thecrankcase. The above-mentioned PAG oil can be used as the oil, forexample.

The position relation in the vertical direction between oil separator 6and compressor 2, is such that oil separator 6 is disposed higher thancompressor 2, which means that compressor 2 is lower than oil separator6, so that the oil separated by oil separator 6 can be smoothly returnedto compressor 2 under its own weight.

The site from oil separator 6 to expansion valve 4 in the refrigerationcycle usually becomes a liquid line, and at a certain position in theliquid line sight glass 8, through which internal behavior of therefrigerant can be observed, is provided.

Because the oil forcibly separated by oil separator 6 is returned tocompressor 2 through oil return line 7, lubrication state of compressor2 is kept in a state good enough, and the durability for a long term canbe ensured. Further, because the oil forcibly separated by oil separator6 is not supplied into downstream side of oil separator 6 in therefrigeration cycle route, the fear to cause a heat transfer obstructionby the oil adhesion in a heat exchanger, such as evaporator 5 in theshown example, which is located at downstream side can be reduced, andthe refrigeration ability and the coefficient of performance ofrefrigeration cycle 1 can be improved. Furthermore, because the oilforcibly separated by oil separator 6 is not supplied to sight glass 8provided in the liquid line, sight glass 8 is prevented from misting bythe oil, so that the internal behavior of the refrigerant can be surelymonitored so as to surely detect the excess and deficiency of therefrigerant through the monitoring of the refrigerant behavior.

Oil separator 6 can be configured into various kinds of structures. FIG.2-FIG. 4 show structural examples where an oil separator is providedbetween compressor 2 and condenser 3 in the above-mentioned two-phaseseparation region. FIG. 5 shows a desirable structural example where oilseparator 6 is provided at the most desirable position shown in FIG. 1.Some of these structural examples can be combined with each other asdescribed above, because they are no more than examples.

In the example shown in FIG. 2, the refrigerant and the oil deliveredfrom compressor 2 are centrifuged by pipe-shaped centrifugal separationsection 11 provided as a centrifugal separation means in oil separator 6a, so as to be forcibly separated into refrigerant phase 12 and oilphase 13 which is temporarily stored in a temporary storage section forthe oil at the bottom side, and the separated oil is returned throughoil return line 7 to compressor 2 while the separated refrigerant isdelivered to condenser 3.

In the example shown in FIG. 3, the refrigerant and the oil deliveredfrom compressor 2 are forcibly separated into refrigerant phase 22 andoil phase 23 which is temporarily stored in a temporary storage sectionfor the oil at the bottom side by collision separation section 21 as acollision separation means, which is provided in oil separator 6 b andseparates the refrigerant and the oil by the colliding between therefrigerant and the oil, so that the separated oil is returned throughoil return line 7 to compressor 2 while the separated refrigerant isdelivered to condenser 3.

In the example shown in FIG. 4, the refrigerant and the oil deliveredfrom compressor 2 are forcibly separated into refrigerant phase 32 andoil phase 33 which is temporarily stored in a temporary storage sectionfor the oil at the bottom side by trap separation section 31 as a trapseparation means, which is provided in oil separator 6 c and separatesthe refrigerant and the oil by trapping the oil from the refrigerant andthe oil, so that the separated oil is returned through oil return line 7to compressor 2 while the separated refrigerant is delivered tocondenser 3.

In the example shown in FIG. 5, the refrigerant and the oil deliveredfrom condenser 3 are centrifuged by pipe-shaped combined centrifugalseparation section and lifting tube 41 provided as a centrifugalseparation means in oil separator 6 d, which corresponds to oilseparator 6 shown in FIG. 1, so as to be forcibly separated into liquidrefrigerant phase 42 and oil phase which is temporarily stored in atemporary storage section for the oil at the bottom side, and furtherthe oil is trapped and retained by oil trap separation section 44provided in the temporary storage section for the oil from therefrigerant lifted by combined centrifugal separation section andlifting tube 41, so that the refrigerant and the oil are forciblyseparated as preventing the oil from flowing out together with therefrigerant flow. While the separated oil is returned through oil returnline 7 to compressor 2, the separated refrigerant is delivered toexpansion valve 4 or to the subcooled region (liquid refrigerant) incondenser 3 where condenser 3 is the above-described subcool condenser.

Thus the oil separation means itself can be configured in variousstructures, as depending on a place to provide in the two-phaseseparation region.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The refrigeration cycle according to the present invention is applicableto any refrigeration cycle where the new refrigerant R1234yf may beused, and is suitable for a refrigeration cycle used in an automotiveair conditioning system.

EXPLANATION OF SYMBOLS

-   1: refrigeration cycle-   2: compressor-   3: condenser-   4: expansion valve as decompression/expansion means-   5: evaporator-   6, 6 a, 6 b, 6 c, 6 d: oil separator as oil separating means-   7: oil return line-   8: sight glass-   11: centrifugal separation section as centrifugal separation means-   12, 22, 32: refrigerant phase-   13, 23, 33, 43: oil phase-   21: collision separation section as collision separation means-   31: trap separation section as trap separation means-   41: combined centrifugal separation section and lifting tube-   44: oil trap separation section

1. A refrigeration cycle having a compressor for compressingrefrigerant, a condenser for condensing compressed refrigerant, adepressurizing/expanding means for depressurizing and expandingcondensed refrigerant, and an evaporator for evaporating depressurizedand expanded refrigerant in this order in a refrigerant flowingdirection, characterized in that R1234yf is used as said refrigerant,and an oil separating means for forcibly separating said refrigerant andoil one from the other is provided in a two-phase separation region, inwhich said refrigerant and said oil exist in a separate state withoutbeing dissolved with each other, present in a route from an exit side ofsaid compressor to said depressurizing/expanding means.
 2. Therefrigeration cycle according to claim 1, wherein said oil separatingmeans is provided at a position between said condenser and saiddepressurizing/expanding means.
 3. The refrigeration cycle according toclaim 1, wherein an oil return line for returning oil separated by saidoil separating means to said compressor is provided between said oilseparating means and said compressor.
 4. The refrigeration cycleaccording to claim 1, wherein a sight glass capable of monitoringbehavior of said refrigerant present inside is provided at a downstreamside of said oil separating means as viewed in a refrigerant circulationdirection.
 5. The refrigeration cycle according to claim 1, wherein saidoil comprises polyalkylene glycol.
 6. The refrigeration cycle accordingto claim 1, wherein said oil separating means is disposed at a higherposition than said compressor in a vertical direction.
 7. Therefrigeration cycle according to claim 1, wherein said oil separatingmeans has a centrifugal separation means for separating said refrigerantand said oil by centrifuging said refrigerant and said oil.
 8. Therefrigeration cycle according to claim 1, wherein said oil separatingmeans has a collision separation means for separating said refrigerantand said oil by a collision of said refrigerant and said oil.
 9. Therefrigeration cycle according to claim 1, wherein said oil separatingmeans has a trap separation means for separating said refrigerant andsaid oil by trapping said oil from said refrigerant and said oil. 10.The refrigeration cycle according to claim 1, wherein said oilseparating means has a centrifugal separation means for separating saidrefrigerant and said oil by centrifuging said refrigerant and said oiland a trap separation means for separating said refrigerant and said oilby trapping said oil from said refrigerant and said oil.
 11. Therefrigeration cycle according to claim 1, wherein said oil separatingmeans has a collision separation means for separating said refrigerantand said oil by a collision of said refrigerant and said oil and a trapseparation means for separating said refrigerant and said oil bytrapping said oil from said refrigerant and said oil.
 12. Therefrigeration cycle according to claim 1, wherein a temporary storagesection for separated oil is provided at a lower position in a verticaldirection in said oil separating means.
 13. The refrigeration cycleaccording to claim 1, wherein an exit for separated oil is provided at alower end in a vertical direction of said oil separating means.
 14. Therefrigeration cycle according to claim 1, wherein said refrigerationcycle is used in an air conditioning system for vehicles.